In the past, there is known a technique for switching a conveying path in order to convey a sheet subjected to decoloring processing to any one of plural predetermined conveyance destinations.
However, in detecting the length of a sheet while conveying the sheet, depending on the length of a sheet to be subjected to decoloring processing, the leading end of the sheet reaches a branching point of a conveying path before the total length of the sheet is found. In such a case, the conveying path cannot be switched.